How worrisome! Sending {{{vibes}}} your way for your rabbit.
Is he taking the critical care alright? I would hope you would see some poo soon once that has moved through his gut.
Could the blood be from the syringe feeds? Im remembering a vet trying to give one of my rabbits water by mouth once and she (the rabbit) was so stubborn. It ending up causing her mouth to bleed a bit. Have you tried offering the CC in a bowl?
Is your rabbit drinking at all?
I wonder if an alternative to metacam would be worthwhile? As some buns are sensitive and it can suppress appetite.
I heard that vitamin B water can help with appetite. That might be worth a try.
What sort of foods have you been offering him? If he’s snubbing the usual favourites, I would get some things he’s rarely had before. It’s weird how rabbits might go for these things when the gut is off.
Should I ask for an Xray?
It’s probably worth asking the vet about but they may deem him too unstable to anaesthetise. They might be able to do a conscious xray of his abdomen, but Im not sure they’d be able to do that for head x-rays. Definitely worth a discussion with your vet, regardless.
Has the vet been able to feel any food in his gut at all? My concern now would be build up of bad bacteria and toxins in the gut. You may have to give an additional medication to try circumvent that.